The invention relates to a positive displacement pump with a pump housing which has inlet and outlet openings in which an endless transportation belt revolves around at least two reversing rollers of which at least one is driven, and whereby the endless belt has recesses on at least one of its surfaces which, during the revolutions of the belt form conveying chambers of periodically variable volumes.
Positive displacement pumps of this type have already been known. A pump with an endless flat belt has been known f. ex. from the U.S. Pat. No. 2,355,928, which revolves around two reversing rollers and which on its inside has V-shaped notches which serve as conveying chambers of variable volumes. The liquid that is to be conveyed is fed to the space between the two reversing rollers, it there reaches the V-shaped notches of the belt, and upon running up said belt it is squeezed out onto one of the rollers laterally from the notches. The liquid reaches a chamber which is connected with an outlet line.
From the British Pat. No. 818,091, a similar positive displacement pump has been known in the case of which an inside toothed V-belt is used instead of a flat belt, which revolves around two pulleys. Since the pulleys will not permit a lateral emergence of the conveyed liquid from the V-shaped notches, said liquid must leave radially toward the inside and must be fed via the pulley shaft developed as a housing shaft to an outlet line.
These known constructions of positive displacement pumps have the disadvantage that the conveyed quantity is limited because of the tight outlet channels and in that it cannot be used for the conveyance of contaminated liquid or liquid enriched otherwise with solid bodies. The solid bodies which have entered the conveying chambers are forced to the outside under the action of the centrifugal forces in the chambers and they can no longer emerge on the places provided for this purpose. They remain jammed in the chambers of the revolving belt and they will cause a quick destruction of the latter. In addition the narrow outlet chambers and channels necessary in the case of these pump constructions are quickly plugged up. A further disadvantage of this type of pump construction is that the liquid that is to be conveyed must be fed to the inside space between the reversing rollers where it also enters the V-shaped notches of the strand of the belt which is not intended for conveyance. In the case of the revolution of this strand of belt around the counter roller, whirls develop in the housing which lead to cavitation phenomena and to losses in the degree of effectiveness.